What everybody says:
x Airbus A32S seats are very spacy and roomy in Y-class
x Boeing B737 seats tend to be quite cramped

My experience being 6'5'':
x Airbus A319 of BA: seats in the back are very cramped (my knees hurted after a 50 minuts flight)
x Boeing B737-200 of Ryanair with 29'' seat pitch: much more comfortable in terms of seat pitch

Does anybody know how this is possible? Because I wanted to double-check this, I tested the SN A319 a few months ago:

x the seats that can be converted to C-class are very spacy
x once you have passed the wing, they are extremely cramped (I wouldn't be able to fly 4 hours in them)

I also tested an AF A320 a few months ago (did not fly on it, only tested the seats), and this one gave me the same expression.

I remember a flight on a VEX B733 in 2002 where I also had a lot of legspace. Also on the BA B752 where everybody complains about legspace, I had comfortable flights.

Can anybody give me some more explanations about B737 + A32S and seats?

TG992 hit the nail right on the head...although it should be pointed out that narrowbody Airbuses are 7 inches wider than narrowbody Boeings which would probably translate to a slightly wider seat generally among most Airbuses...